The influence of four fungicide formulations on the degradation rate and selective extractability of carbofuran in the soil

‘Soil was incubated for 18 weeks with carbofuran alone (control) or in combination with Manate (maneb), Apron (metalaxil + mancozeb), Ridomil Special (metalaxil + maneb) and Pomarsol (TMTD) which were added to the soil at high (250 ppm) and lower (25 ppm) concentration. In the presence of fungicides the half‐life time value for carbofuran in the soil was 1.2 to 3 times higher than in the control depending on the nature of the fungicide and its concentration. The degradation rate, as reflected from the degradation ratio R measured at weekly time intervals, was greatly affected by the presence of the fungicides: at the lower concentration the R values were much lower only during the first weeks of incubation , whereas at the higher fungicide concentration this inhibitory effect on the degradation rate appeared to be very persistent. The extraction of the soil samples at the end of the incubation period has been performed using either water or a benzene‐acetone mixture as solvents. The differential extractability, which is linked to the insecticide bioavailability in the soil environment, has been shown to be influenced by the presence of the fungicides: at high application rate the carbofuran was relatively better extracted with water than at lower application rate or in the absence of fungicides.